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Transcript: Welcome to our third CCDA lab. We’ll be considering internet link redundancy options and we’ll see how we can achieve both active-active and active-standby ISP configuration. So in this lab, we have two routers: R1 and the ISP router. So R1 would act like the organization’s router connected to the ISP’s router via the fe0/1 interface. And this is like the LAN. So we have two hosts on the LAN.

So let’s take a look at the configuration on R1. So show run. And you notice that we have interface configuration. So this is the LAN 10.0.10.1, IP NAT inside, and this is the WAN. 192.0.2.2 IP NAT outside. So I just use the NAT so that when the guys on the inside … so, look at this access list here. So it matches IP from anybody from the LAN going to anywhere. And then that access list is used in a route map, and that route map is used in a NAT statement.

So basically they get translated to the IP address of the 0/1 interface … fe0/1 interface. Which is 192.0.2, right? Good. And notice that all we have is a default route, right? So a default route to the ISP router. So the ISP router, if will come here, and we’ll do a show IP interface. [inaudible 00:01:27]. That’s the IP address right there, and we use this to … IP address is to simulate something on the internet.

Right. So that’s all that we have. That’s the only configuration that we have on R1 and now let’s test. So if we come to the VPC-1, if I ping, say, 8.8.8, right? So it goes through, right? Now of course it goes through and there’s only one link. So if anything happens to this link, then it means that this whole … the organization’s network goes down. Because they only have one link to the ISP, that’s to the internet.

Now one thing we could do, let’s simulate another scenario where you have two links, right? Two links but to the same ISP. You could have complex scenarios like two routers connected to the same ISP or different ISPs but in this case we’ll keep it simple. So I’m going to add a serial interface, so this guy, okay. And let’s configure R1. So R1, the serial interface of R1, let’s give it an IP address of 2.6 … 252 … no shut. I also have to make this IP nat outside. And it means I will have to configure … so let’s take something from here. Let’s do a show run … not router map. Route map.

Okay, so let’s use this guy. We’ll use that … we’ll make it two, match same IP address but we’ll match the serial 1/0 interface. And here, we would say two, and then the interface, will be serial 1/0 overload also. Alright. Now the last thing we need to configure is the route … the IP route statement. Now, you could use this link, you could use both links at the same time, so like active-active, or you could have an active-standby. So maybe this one is your primary link and this one goes down, and this one comes back up.

So let’s try the active-standby … let’s try the active-standby first. So R1 … and then all we have to do is to specify a higher metric than the other one that we have. So if I do a show run right now … IP route. Alright. So this is the first one that we have, that’s through the FastEthernet 0/1 interface, and this is the second one. So it has a higher metric. So if I do a show IP route, I would only see the one through the FastEthernet 0/1 interface.

So what we have created here is called a floating static route. If this route goes down, then this one will be stored in the routing table, right? So let’s come to the ISP. Let’s just debug IP ICMP, and come here, we’ll ping … So as you can see it’s using the IP address of the fe0/1 interface. So let’s shutdown the interface and see. So if I shut it down, then if I do a show ip route, what you’ll see is that this other static route … so the floating static route has been installed.

So if I ping again … let’s just wait for some time … Okay, so it seems there’s something I haven’t configured. Of course I haven’t configured it on this side. So 1/0 IP address is 192.0.2.5 … 252. Okay, let’s try it out again. Okay, cool. Alright so now you notice that the IP address is now the serial interface. So basically that’s how you use an active-standby scenario. If this one goes down, this one will be still … If that one comes back up … so let’s come back to R1, and let’s do no shut. If it comes back up, the previous routes will be installed back into the routing table because it has a better metric. And if we ping again … you see that it’s back to the other guy, yeah? Alright.

But what if we want an active-active scenario? In that case, all we have to do is remove the metric that we added here. So let me remove this guy, and we’ll just remove the metric. So right now, if I check to a show ip route, you’ll see that it will try to load balance between both of the interfaces. So serial 1 and the fe0/1. Now, we need to keep in mind that the way the Cisco router does routing is a bit different. So it doesn’t do by … by default it doesn’t do per packet load balancing, it actually does per destination.

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So you may notice that even though both of these … even though the default router’s pointing to two different guys, it’s only going to use one for a particular destination. So if I come to this guy, if I ping 8.8, right now it uses 2.2. Let’s try it’s ping another destination and see. So if I ping 9.9 … Now notice it’s still using .2. So let’s bring up this other guy and let’s see if it’s going to use the other link. So 8.8, let’s come to the ISP.

Yeah, so as you can see, this other guy is using this other link. So you can see that both links are being used but not just for the same traffic flow, right? So that’s pretty cool and if you lose anyone of the interfaces then traffic will fall back to the one that is available. So for example if I lose 1.0, and I try to ping, this is still fine and this one is still fine, alright? So as you can see it goes back to using the one that is available, right, cool.

Adeolu Owokade is a technology lover who has always been intrigued by Security. He has multiple years of experience in the design, implementation and support of network and security technologies. He's a CCIE (Security) with a new found love in writing.

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